Neutral beam etching of Cu-containing layers in an organic compound gas environment

ABSTRACT

A method and apparatus for dry etching pure Cu and Cu-containing layers for manufacturing integrated circuits. The invention uses a directional beam of O-atoms with high kinetic energy to oxidize the Cu and Cu-containing layers, and organic compound etching reagents that react with the oxidized Cu to form volatile Cu-containing etch products. The invention allows for low-temperature, anisotropic etching of pure Cu and Cu-containing layers in accordance with a patterned hard mask or photoresist.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to the field of semiconductor processingand more particularly to a method and apparatus for anisotropic etchingand patterning of pure Cu and Cu-containing layers used in integratedcircuits.

Description of the Related Art

Copper (Cu) is emerging as the metal of choice in a wide variety ofsemiconductor applications. Lower electrical resistivity, coupled withimproved electromigration performance and increased stress migrationresistance are important material properties that favor the use of Cuover aluminum (Al) in interconnect lines and contacts. The lowerelectrical resistance is critical since it allows signals to move fasterby reducing the RC time delay. The superior resistance toelectromigration, a common reliability problem in Al lines, means thatCu can handle higher power densities. An equally important benefit ofusing Cu over Al is that the manufacturing cost for a Cu metallizationscheme can be lower due to new processing methods that reduce the numberof manufacturing steps and alleviate the need for some of the mostdifficult steps.

The capability to process substrates anisotropically permits theproduction of integrated circuit features at precisely defined locationswith sidewalls that are essentially perpendicular to the surface of amasked overlayer. The introduction of Cu into multilevel metallizationarchitecture requires new processing methods for Cu patterning. BecauseCu is difficult to dry etch, new process schemes have been developed forCu patterning.

The damascene approach is based on etching features in the dielectricmaterial, filling them with Cu metal, and planarizing the top surface bychemical mechanical polishing (CMP). Dual damascene schemes integrateboth the contacts and the interconnect lines into a single processingscheme. However, Cu CMP technology is challenging and it has difficultydefining extremely fine features. In addition, CMP suffers fromyield-detracting problems of scratching, peeling, dishing and erosion.

An alternative to the damascene approach is patterned etching of a Culayer. The patterned etch process involves deposition of a Cu layer on asubstrate, the use of a patterned hard mask or photoresist over theCu-containing layer, patterned etching of the Cu layer using a reactiveion etching (RIE) process; and deposition of dielectric material overthe patterned Cu-containing layer. Patterned etching of Cu can haveadvantages over damascene processes since it is easier to etch fine Cupatterns and then deposit a dielectric layer onto the Cu pattern, thanit is to get barrier layer materials and Cu metal to adequately fillsmall feature openings in a dielectric film.

Patterned etching using RIE processes is characterized by relatively lowpressures and high ion bombardment energies. While ion bombardment isneeded to achieve the desired degree of etch anisotropy, it is alsoresponsible for secondary damage to the underlying microstructure. Assemiconductor devices have become increasingly more integrated and newadvanced materials, such as copper and low-k dielectric materials, havebeen introduced to improve the circuit properties, the damage caused byfabrication processes presents an increasingly serious problem. Aleading reason for damage formation is essentially the incidence ofenergetic particles, such as ions and UV photons, from the plasmaenvironment to the substrate surface.

The primary etch reagent for removing Cu layers is traditionally achorine-containing gas in gas mixture that includes argon (Ar). Removalof pure Cu layers and Cu-containing layers with high Cu-content usingchlorine plasma essentially involves physical sputtering of thelow-volatility CuCl_(x) surface layer by energetic ions in the plasma.The Cu removal rates are very low when using this method and anotherdrawback is that the sputtered CuC_(x) coats the chamber walls and thisrequires periodic cleaning of the etching chamber. An equally seriousproblem is encountered when high-aspect-ratio features are etched inchlorine plasma and the sputtered CuCl_(x) products redeposit on thefeature sidewalls where the effects of physical sputtering are reduced.

When the abovementioned chlorine-based etching process is carried out atelevated temperatures (>200° C.) to increase the volatility of thereacted Cu-containing layer, corrosion can occur due to the accumulatedCuCl_(x) etch residues on the surface. If these residues are not removedby a post-etch cleaning step, they can cause continuing corrosion of theCu even after the application of a protective layer over the etchedfeatures.

Other energy sources have been suggested to increase the etching rate.These approaches include exposing the etching surface to UV or IR lightsources to accelerate desorption of CuCl_(x) from the etching surface.However, these approaches are not practical for semiconductor batchprocessing of large substrates due to poor etch uniformity, high costand added equipment complexity, and reliability problems.

Accordingly, it is desirable to develop a method for anisotropic etchingin semiconductor manufacturing using plasmas that are essentially freeof energetic ions and photon particles. Such particles are ordinarilyrequired to achieve anisotropic etch with atomic oxygen plasmas in theprior art, but cause secondary damage to the underlying substrate.Furthermore, the reaction products should be highly volatile and easilyremoved from the etched substrate. In addition, the aforementionedlimitations that are encountered when etching Cu-containing layers usingconventional chlorine chemistry, show that there is a need for new lowtemperature dry etching methods in semiconductor manufacturing usingchemical approaches that do not involve chlorine-based reactants.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and anapparatus for anisotropic dry etching of pure Cu layers andCu-containing layers used in integrated circuits.

The above and other objects are achieved, according to the presentinvention, by providing a method and an apparatus that uses adirectional beam of high kinetic energy (hyperthermal) neutral O-atomsto anisotropically oxidize Cu layers, and an etching gas comprising anorganic compound gas such as CH₃COOH that readily reacts with theoxidized Cu layers to form volatile Cu-containing etch products. Thehigh directionality of the O-atom beam allows for anisotropic etching ofthe Cu layers in accordance with a patterned hard mask or photoresist.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a flowchart for etching a Cu-containing layer in accordancewith the present invention;

FIGS. 2a-2d show a schematic cross-sectional representation ofanisotropic etching of Cu-containing layers in accordance with thepresent invention;

FIG. 3 shows a schematic cross-sectional representation of anisotropicetching of Cu-containing layers in accordance with the presentinvention;

FIG. 4 shows a processing system according to a preferred embodiment ofthe present invention;

FIG. 5 shows an example of an organic compound gas supply unit in theetching apparatus of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views.

In general, the present invention pertains to a method and an apparatusfor etching pure Cu and Cu-containing layers in manufacturing integratedcircuits. The method uses a directional beam of high kinetic energyO-atoms to oxidize the Cu layers, and an etch reagent that formsvolatile Cu-containing etch products when reacted with the oxidized Culayers.

Importantly, the etch reagent reacts very slowly with unoxidized Cu onfeature sidewalls, but reacts readily with oxidized Cu surfaces at lowtemperatures. Therefore, in order to achieve anisotropic etching andavoid undercutting of etch features, the oxidation rate of Cu on thevertical sidewalls of the etch features must be substantially slowerthan the oxidation of Cu on the horizontal surfaces. This is achievedusing a directional O-atom beam.

The directional beam is preferably a hyperthermal beam of neutralO-atoms that has high kinetic energy and can be produced with lowdivergence from the substrate normal, thereby allowing production ofmasked structures with reduced ion damage and charge build-up problemsoften encountered in plasma processes.

In general, hyperthermal atomic beams contain neutral atoms that havehigh kinetic energy (E_(k)≥1 eV) compared to thermalized atoms(E_(k)˜0.05 eV) produced by conventional glow discharge devices, such asplasma ashers and sputter etching apparatus. The kinetic energy ofhyperthermal atomic beams can be as high as several hundred eV.

The use of hyperthermal O-atom beams to oxidize and etch films has beenshown to result in reduced ion bombardment damage and charge-induceddamage that is commonly observed during plasma etching processes, suchas reactive ion etching (RIE). For example, hyperthermal O-atoms havebeen used for anisotropic etching in semiconductor manufacturing,particularly in the areas of photoresist stripping and multilayerlithography applications, with little or no secondary damage to theunderlying substrate.

Koontz and Cross in U.S. Pat. No. 5,271,800 entitled “Method foranisotropic etching in the manufacture of semiconductor devices,”disclose a method for anisotropic etching of a hydrocarbon polymercoating using a beam of hyperthermal atomic oxygen, to generate adesired pattern on a semiconductor wafer. The hyperthermal beam haskinetic energy in the range between about 0.2 eV to 20 eV and isproduced using a continuous optical discharge laser.

In the current invention, the use of a hyperthermal beam of neutralO-atoms to oxidize Cu layers and Cu-containing layers and subsequentreaction of the oxidized layers with etch reagents to form Cu-containingetch products, allows for anisotropic etching at low substratetemperatures. In one embodiment, the hyperthermal beam of O-atoms isgenerated in a separate chamber from the processing (etching) chamberand the beam contains only neutral O-atoms when it enters the processingchamber. Alternatively, the O-atom beam is generated inside theprocessing chamber. The etch reagent is introduced into the processingchamber using effusive sources and is therefore not exposed to a plasmasource that could result in deleterious decomposition of the etchreagent prior to reaction with the oxidized Cu layers.

FIG. 1 is a flowchart for etching a Cu-containing layer in accordancewith the present invention. Step 100 provides a surface having aCu-containing layer to be etched in a process chamber. In step 102, abeam of hyperthermal oxygen atoms is generated that is capable ofanisotropically oxidizing the Cu-containing layer. The beam of neutralO-atoms is exposed to the Cu-containing layer in step 104 and anoxidized Cu-containing layer is formed in step 106. An etching reagentcapable of reacting with the oxidized Cu-containing layer is introducedinto the process chamber in step 108. Volatile Cu-containing etchingproducts are formed from the reaction of oxidized Cu-containing layerswith the etch reagent in step 110 and are removed from the Cu-containinglayer in step 112. Desorption of the etching products from the etchingsurface is aided by surface bombardment of the energetic O-atoms. TheCu-containing layer is exposed to the beam of O-atoms and the etchinggas for a time period that enables desired etching of the Cu-containinglayer.

FIGS. 2a-2d show a schematic cross-sectional representation ofanisotropic etching of Cu-containing layers in accordance with thepresent invention. FIG. 2a shows a partially completed integratedcircuit. The segment 200 comprises a substrate 210, a Cu-containinglayer 220, and a hardmask or photoresist material 230 completes thestructure. In order to achieve anisotropic etching of a Cu-containinglayer, a resist material overlying the Cu-containing layer is requiredthat is resistant to a beam of hyperthermal 0-atoms. Examples of suchresist materials are polysiloxane-containing resists that are processedusing electron-beam exposure in the presence of a mask overlay. Thesegment 200 in FIG. 2a is processed using conventional patterningmethods known in the art to produce the pattern in FIG. 2b . Furtheranisotropic etching of the structure in FIG. 2b according to the presentinvention etches the Cu-containing layer 220 While preserving thevertical geometry of the structure defined by the photoresist pattern230′, forming the structure shown in FIG. 2c . Continued processing asis conventional in the art, removes the remaining photoresist pattern230′, resulting in the patterned Cu-structure 220′ shown in FIG. 2d.

FIG. 3 shows a schematic cross-sectional representation of anisotropicetching of Cu-containing layers in accordance with the presentinvention. FIG. 3 schematically illustrates characteristics of theetching process that allow for anisotropic etching of Cu-containinglayers. The segment 300 shows a partially completed integrated circuitthat comprises a Cu-containing layer 310 overlaying a substrate 320 anda photoresist pattern 330 overlying the Cu-containing layer 310.Anisotropic etching of the structure in FIG. 3 removes the Cu-containinglayer 310 while preserving the vertical geometry of the structuredefined by the photoresist pattern 330.

The neutral O-atoms in a hyperthermal beam are schematically representedby arrows 340 in FIG. 3. A beam of hyperthermal O-atoms that has a lowdivergence from the substrate normal is depicted using near verticalarrows. The directionality and high kinetic energy of the O-atomsresults in elastic forward scattering from the vertical surfaces(sidewalls) 350 and therefore low probability of sidewall oxidation. Inother words, the residence time of the O-atoms on the sidewalls is tooshort and the kinetic energy in the direction normal to the sidewalls isinsufficient to result in oxidation of the sidewalls 350. In contrast,O-atoms impinging on the horizontal surfaces have enough kinetic energyand a residence time that is long enough to form an oxidized Cu layer360. An etching gas containing the etch reagent 370 is introduced intothe etching chamber separate from the O-atom source using effusivenozzles and the interaction of the etch reagent 370 with the segment 300is therefore isotropic. The etch reagent 370 is chosen so that it doesnot react with unoxidized Cu on the sidewalls 350.

In contrast, when the etch reagent 370 adsorbs onto the oxidized Culayer 360 forming the adsorbed etch reagent 380, it reactsspontaneously, even at low temperature, with the oxidized Cu layer. Inaddition to exposure to the etch reagent 370, the horizontal surfaces ofCu layer 360 are under constant energetic O-atom bombardment 340, which,in addition to oxidizing the surface, further aids desorption of etchproducts 390 from the surface and allows etching of Cu-containing layersat low temperatures.

The kinetic energy of the O-atoms affects the oxidation of thehorizontal surfaces. When O-atoms with high kinetic energy interact withthe horizontal surfaces, the O-atoms penetrate the surface layer, loosetheir kinetic energy (become thermalized) as they become embedded in thesurface layer, and thereby oxidize the surface layer. If the kineticenergy is below a certain threshold energy, the O-atoms are more likelyto “bounce back” without becoming thermalized, and this can result inundesired sidewall oxidation and sidewall etching.

Process conditions that enable the desired etching of the Cu-containinglayer in the current invention may be determined by directexperimentation and/or design of experiments (DOE). For example,adjustable process parameters can comprise the kinetic energy of theO-atoms in the hyperthermal beam, substrate temperature, processpressure, choice of process gases and relative gas flows of the processgases.

The etch reagent gas is preferably an organic compound gas. As for theorganic compound, it is preferable to use one that can be supplied as itis or in a gaseous state by heating to the plasma processing systemmaintained in a vacuum state. Typically, an organic acid is used. As forthe organic acid, it is preferable to use a carboxylic acid representedby an acetic acid (general formula: R—COOH, R being hydrogen orstraight-chain or branched-chain alkyl or alkenyl of C1to C20,preferably methyl, ethyl, propyl, butyl, pentyl, or hexyl). Thecarboxylic acid other than the acetic acid may include formic acid(HCOOH), propionic acid (CH₃CH₂COOH), butyric acid (CH₃(CH₂)₂COOH),valeric acid (CH₃(CH₂)₃COOH) or the like. Among the carboxylic acids,the formic acid, the acetic acid, and the propionic acid are morepreferably used.

When the organic compound is acetic acid, the reaction between copperoxide and acetic acid is accelerated, and volatile Cu(CH₃COO) and H₂Oare generated. As a consequence, copper oxide molecules are separatedfrom the Cu film. The same reaction occurs in the case of using anotherorganic compound (organic acid) such as formic acid or propionic acidother than acetic acid. As a result, the Cu film is etched.

In one embodiment, the etch reagent 370 can comprise chemical compoundssuch as CH₃COOH. The spontaneous reaction between Cu_(x)O and CH₃COOHforming a volatile Cu product has been published in journals. The methodof using a directional energetic O beam (Neutral Beam) to causeanisotropic Cu etching (with a hardmask) in a hfacH ambient (and moregenerally, an acid ambient) is known. However, the present inventorshave discovered that the reactivity of Cu_(x)O with CH₃COOH is muchhigher than that with hfacH. For example, in an ambient pressure on theorder of 1E(−5) torr of CH₃COOH and room temperature substrate, a veryhigh and manufacturing worthy removal rate of CIO is obtainable. Forexample, an ambient pressure of 3E(−5) torr of CH₃COOH and anisotropichyperthermal O, e.g., 100 eV forms Cu_(x)O by the “sub-plantation” ofthe anisotropic hyperthermal O.

The net surface reactions between CH₃COOH and oxidized Cu can be writtenas:CuO+2CH₃COOH→Cu(CH₃COO)₂+H₂O  (1)CU₂O+4CH₃COOH→2Cu(CH₃COO)₂+H₂O+H₂  (2)According to Eqs. (1) and (2), CH₃COOH reacts with oxidized Cu and formsCu, and volatile Cu(CH₃COO )₂+H₂O etching products. Therefore, whenCH₃COOH is selected as the etch reagent 370 in FIG. 3, the volatile etchproducts 390 are Cu(CH₃COO)₂ and H₂O). The Cu etch product in Eq. (2)can undergo oxidation and subsequent reaction with CH₃COOH according toEqs. (1) or (2). Cu(CH₃COO)₂ is volatile at low temperatures and doesnot significantly redeposit on sidewalls of Cu etch features or on theprocess chamber walls.

An inert gas can be added to any one of the aforementioned process gaschemistries. The inert gas may include at least one of argon, helium,krypton, xenon, and nitrogen. For example, the addition of inert gas tothe process chemistry is used to dilute the process gas or adjust theprocess gas partial pressure(s).

Transport of the gaseous CH₃COOH etching gas to the processing chambermay be achieved using a delivery system that can comprise a bubblersystem and a mass flow controller (MFC). The bubbler system can be usedwith or without a carrier gas such as argon (Ar). When a carrier gas isused, it is bubbled through the CH₃COOH liquid and becomes saturatedwith the CH₃COOH vapor. The partial pressure of the CH₃COOH vapor in theprocess chamber is controlled by the temperature of the CH₃COOH liquidin the bubbler. Exemplary gas flow rates of CH₃COOH and a carrier gasare less than 1000 sccm, preferably being less than 500 sccm.Alternatively, a liquid injection system can be used to deliver theCH₃COOH to the processing chamber. The handling and use of etch reagentssuch as CH₃COOH reagents in this invention is well known in the art.

Nguyen and Chameski in U.S. Pat. No. 6,284,052 entitled “In-situ methodof cleaning a metal-organic chemical vapor deposition chamber,” describea method to clean the interior surfaces, and especially the chuck, of ametal deposition chamber. The method first oxidizes the surface to becleaned with an oxygen plasma, and then removes the oxide products as avapor with the use of CH₃COOH.

Koide et al. in U.S. Pat. No. 5,993,679 entitled “Method of cleaningmetallic films built up within thin film deposition chamber,” describe amethod that includes an oxidation step to oxidize a metallic film, acomplexing step to complex the oxide film, and a sublimations step tosublimate the complex. The conditions of these cleaning steps are set sothat the oxidations step is the rate determining step.

The focus of the current invention is to enable anisotropic etching ofCu layers and Cu-containing layers for patterning multilayer structures.The main purpose of the above-mentioned methods is to clean and removemetallic films from processing chambers through the formation ofvolatile etch products from the reaction of oxidized metal films withCH₃COOH.

FIG. 4 shows a processing system according to a preferred embodiment ofthe present invention. The processing system 600 comprises a processchamber 605 and an O-atom beam source 610. The process chamber 605comprises a substrate holder 615, upon which a substrate 620 to beprocessed is affixed, a gas injection system 625 for introducing processgases 630 to the process chamber 605, and a vacuum pumping system 635.For example, a gate valve shown) is used to throttle the vacuum pumpingsystem 635. Process gases 630 are introduced via the gas injectionsystem 625 and the process pressure is adjusted. The gas injectionsystem 625 allows independent control over the delivery of process gases630 to the process chamber from ex-situ gas sources. The process gases630 can comprise etch reagents and inert gases. The O-atom beam source610 generates a directional beam 640 of high kinetic energy neutralO-atoms that are introduced to the process chamber 605. The beam ofO-atoms 640 etches a Cu-containing layer on the substrate 620 in thepresence of the etch reagents as described in FIGS. 1-3.

Substrate 620 is transferred into and out of process chamber 605 througha slot valve (not shown) and chamber feed-through (not shown) viarobotic substrate transfer system where it is received by substrate liftpins (not shown) housed within substrate holder 615 and mechanicallytranslated by devices housed therein. Once the substrate 620 is receivedfrom the substrate transfer system, it is lowered to an upper surface ofthe substrate holder 615.

In an alternate embodiment, the substrate 620 is affixed to thesubstrate holder 615 via an electrostatic clamp (not shown).Furthermore, the substrate holder 615 further includes a cooling systemincluding a re-circulating coolant flow that receives heat from thesubstrate holder 615 and transfers heat to a heat exchanger system (notshown), or when heating, transfers heat from the heat exchanger system.Moreover, gas may be delivered to the backside of the substrate toimprove the gas-gap thermal conductance between the substrate 620 andthe substrate holder 615. Such a system is utilized when temperaturecontrol of the substrate is required at elevated or reducedtemperatures. Vacuum pump system 635 preferably includes aturbo-molecular vacuum pump (TMP) capable of a pumping speed up to 5000liters per second (and greater) and a gate valve for throttling thechamber pressure.

A controller 645 includes a microprocessor, a memory, and a digital I/Oport capable of generating control voltages sufficient to communicateand activate inputs to the processing system 600 as well as monitoroutputs from the processing system 600. Moreover, the controller 645 iscoupled to and exchanges information with the process chamber 605, theO-atom beam source 610, the process monitor system 650, the gasinjection system625 and the vacuum pump system 635. A program stored inthe memory is utilized to control the aforementioned components of aprocessing system 600 according to a stored process recipe. One exampleof controller 645 is a digital signal processor (DSP), model numberTMS320, available from Texas Instruments, Dallas, Tex.

The process monitor system 650 can comprise, for example, a massspectrometer system to measure gaseous species, such as etch reagentsand etch by-products in the processing environment. In general, theprocess monitor system 650 is a versatile diagnostic tool capable ofperforming multiple tasks such as process analysis and endpointdetection. The process monitor system 650, shown in FIG. 4, is attachedto the processing chamber 605. In an alternate embodiment, the processmonitor system is located downstream from the vacuum pump system 635.The process monitor system 650 can he used with controller 645 todetermine the status of the etching process and provide feedback toensure process compliance.

Examples of hyperthermal O-atom sources will now be described. Variousmethods and apparatus have been developed for generating a beam ofneutral hyperthermal O-atoms. The dissociative ionization of molecularoxygen (O₂) supply gas to produce atomic oxygen can be carried out usingoptical laser-induced discharges, DC or AC arcs, inductive coupling,microwave, or electron bombardment discharges, that are usually in aseparate chamber connected to the wafer processing chamber. O-ions thatare formed from the dissociation of O₂ in the plasma are accelerated tothe selected high kinetic energy and then charge neutralized, forming abeam of neutral hyperthermal O-atoms. The charge neutralization of theO-ions can be carried out using a variety of different method. Anexample is electron transfer from interaction of O-ions with metalsurfaces at grazing incidence.

Chen and Yvonne in U.S. Pat. No. 6,331,701 entitled “RF-groundedsub-Debye neutralizer grid,” describe apparatus for generating ahyperthermal beam of neutral O-atoms with kinetic energy ranging from 20eV to 400 eV and a beam diameter of 1 inch to greater than 10 inches forprocessing large substrates. The hyperthermal beam is generated bypassing accelerated oxygen ions from a RF-plasma through a neutralizergrid where the oxygen ions are charge neutralized through forwardsurface scattering. The hyperthermal beam has high flux of neutralO-atoms and a small divergent angle (˜6-3°).

Optical laser-induced discharges can employ pulsed laser radiation as anenergy source for dissociation the supply gas (e.g., O₂) in an expansionnozzle. The expansion creates a hyperthermal beam of neutral reactivespecies (e.g., O-atoms) that can be collimated using an orifice betweenthe expansion chamber and the processing chamber.

An organic compound gas is supplied from an organic compound gas supplyunit into a target chamber. Here, an acetic acid as an organic acid isused as an example of the organic compound. FIG. 5 illustrates anexample organic compound supply unit that may be used in accordance withembodiments of the invention. For example, the organic compound supplyunit may be used as the gas injection system 625 in FIG. 4. As seen, theorganic compound gas supply unit 30 includes an intermediate vessel 36and a tank 37 for storing an organic compound, and a valve 37a isdisposed on a line 36a for connecting the intermediate vessel 36 and thetank 37. The organic compound is supplied from the intermediate vessel36 to the target chamber through the line 32, and the line 32 isprovided with a variable leak valve 38. The intermediate vessel 36 has asensor for detecting the amount of the organic compound therein, e.g., aliquid surface sensor 39, so that the amount of the organic compound inthe intermediate vessel 36 is measured. When the lowering of the liquidsurface is detected by the liquid surface sensor 39, the intermediatevessel 36 is disconnected from the vacuum by the variable leak valve 38and an organic compound is supplied from the tank 37 to the intermediatevessel by opening the valve 37a.

The organic compound (acetic acid) in the reservoir 37 is evaporated,and the evaporated organic compound is supplied to the target chamber.At this time, the evaporation amount of the organic compound (aceticacid) is controlled by controlling an opening degree of the variableleak valve 38. The supply amount of the organic compound gas is set to alevel that allows sufficient organic compound molecules to be adsorbedto the surface of the Cu film formed on the substrate. The pressure inthe target chamber (partial pressure of acetic acid) is preferably about10⁻⁴ Torr to 10⁻⁶ Torr. A pressure gauge may be, e. g. an ion gauge or acapacitance monometer.

As with the embodiments discussed above, the reducing gas comprises anacid such as CH₃COOH, and the reacting gas comprises 02. An inert gassuch as He, Ne, Ar, Kr, and Xe may also be used. Further, the reactinggas and reducing gas may be introduced simultaneously into the plasmaprocessing chamber, in a single-step process, or introduced sequentiallyinto the plasma processing chamber, in a multi-step process.

It should be understood that various modifications and variations of thepresent invention may be employed in practicing the invention. It istherefore to be understood that, within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallydescribed herein.

The invention claimed is:
 1. A method for etching a copper-containing layer on a substrate, comprising: loading a substrate into a processing chamber having a neutral beam source and a substrate holder, the substrate having a copper-containing layer and etch mask formed thereupon; exposing, at a pressure, the copper-containing layer to a directional neutral beam comprising a reacting gas, the reacting gas anisotropically forming a first copper-containing compound on a portion of exposed surfaces of features formed in the copper-containing layer based on directionality of the neutral beam; introducing, at said pressure, a reducing gas comprising a carboxylic acid into the processing chamber, proximate the substrate holder, the reducing gas spontaneously reacting with the first copper-containing compound to form a volatile second copper-containing compound; and pumping the volatile second copper-containing compound from the processing chamber, to anisotropically etch and form a pattern in the copper-containing layer, wherein a temperature of the substrate is maintained at room temperature and said pressure is maintained on the order of 1E(−5) Torr.
 2. The method of claim 1, wherein the carboxylic acid comprises at least one of acetic acid, formic acid, propionic acid, butyric acid and valeric acid.
 3. The method of claim 2, wherein the reducing gas comprises CH₃COOH.
 4. The method of claim 1, wherein the reacting gas comprises O₂.
 5. The method of claim 1, wherein the first copper-containing compound is preferentially formed at the bottom surfaces of features formed in the copper-containing layer.
 6. The method of claim 1, further comprising introducing an inert gas into the processing chamber.
 7. The method of claim 1, wherein the kinetic energy of the reacting gas of the neutral beam is between 1 meV and 1 keV.
 8. The method of claim 1, wherein the kinetic energy of the reacting gas of the neutral beam is between 10 eV and 300 eV.
 9. The method of claim 1, wherein the kinetic energy of the reacting gas of the neutral beam is between 50 meV and 1 eV.
 10. The method of claim 1, wherein the divergence angle of the directional neutral beam of the reacting gas is less than about 20°.
 11. The method of claim 10, wherein the divergence angle of the directional neutral beam of the reacting gas is less than about 10°.
 12. The method according to claim 6, wherein the inert gas comprises at least one of argon, helium, xenon, and nitrogen.
 13. The method of claim 1, wherein said exposing and introducing steps are performed at a same process pressure.
 14. A method for anisotropically etching a Cu-containing layer comprising the steps of: loading a substrate into a vacuum chamber, the substrate comprising a Cu-containing layer overlying a substrate; introducing, at a pressure, a directional beam of neutral oxygen atoms having a kinetic energy between 100 eV and 1 eV; anisotropically oxidizing a portion of the Cu-containing layer by exposure to the beam of oxygen atoms based on directionality of the beam; introducing, at said pressure, a carboxylic acid gas spontaneously forming volatile etch products when reacted with the oxidized Cu-containing layer; and removing the etch products from the oxidized Cu-containing layer to anisotropically etch the Cu-containing layer, wherein a temperature of the substrate is maintained at room temperature and said pressure is maintained on the order of 1E(−5) Torr.
 15. The method according to claim 14, wherein the carboxylic acid gas comprises CH₃COOH.
 16. The method of claim 14, wherein said exposing and introducing steps are performed at a same process pressure.
 17. A method for etching a copper-containing layer on a substrate, comprising: loading a substrate into a processing chamber having a neutral beam source and a substrate holder, the substrate having a copper-containing layer and etch mask formed thereupon; exposing, at a pressure, the copper-containing layer to a directional neutral beam comprising a reacting gas, the reacting gas anisotropically forming a first copper-containing compound on a portion of exposed surfaces of features formed in the copper-containing layer by based on directionality of the neutral beam; introducing, at said pressure, acetic acid gas into the processing chamber, proximate the substrate holder, the acetic acid gas spontaneously reacting with the first copper-containing compound to form a volatile copper-containing compound; and pumping the volatile copper-containing compound from the processing chamber, to anisotropically etch and form a pattern in the copper-containing layer, wherein a temperature of the substrate is maintained at room temperature and said pressure is maintained on the order of 1E(−5) Torr.
 18. The method of claim 17, wherein the first copper-containing compound is preferentially formed at the bottom surfaces of features formed in the copper-containing layer.
 19. The method of claim 17, wherein said exposing and introducing steps are performed at a same process pressure. 